Field of the Invention
The invention relates to a control device for an internal combustion engine. The control device has a magnetic actuator with a coil and an armature, a final control element connected to the armature, a regulating unit for regulating a current in the coil and a measuring device for generating test signals which act on the coil.
A control device including an actuator having a coil, a core and an armature, a final control element and a regulating unit are described in Published European Patent Application EP 0 400 389 A2. To attract the armature to the core, the coil is supplied with an attraction current which has an amplitude that is large enough that the force required to accelerate and move the armature is available through the magnetic flux. When the armature abuts against the core, the current through the coil is limited to a holding current. An amplitude of the holding current is provided so that at least a holding force required to hold the armature on the core is applied through the magnetic flux.
The current through the coil is reset by an on-off controller to the respective theoretical value of the attraction current or of the holding current. In this case, the pulse/pause ratio of the actuation signal is dependent upon the attainment of an upper and a lower threshold value of the current.
The recognition of an instant of impact of the armature on the core has extremely great importance, since in the event of a delayed switch over to the holding current very high losses occur in the coil, which may lead to the thermal destruction thereof.
In the above-mentioned control device, the temporal duration of the pulses of the actuation signal is determined by the regulating unit and is used as an indirect measure of the inductance of the coil, which increases as the spacing between the core and the armature decreases. On this basis, the holding current is predetermined as a theoretical value when the determined time duration is above a limiting value. In this connection, it is a significant disadvantage that the instant of impact of the armature cannot be determined precisely. If the armature impinges on the core shortly before the current reaches its lower threshold value, then the impact cannot be detected until after the following pulse of the actuation signal. Accordingly, high losses arise in the coil, since the current is limited to the holding current too late. The losses can be reduced only in circumstances in which the attraction current has an appropriately low magnitude. However, this brings about an increase in the time which the armature requires to pass from a neutral position to abutment against the core. Accordingly, the final control element can no longer be driven as rapidly. This is a disadvantage, in particular in the case of injection valves or in the case of inlet/exhaust valves of an internal combustion engine.